Alginic acid, and alginate, such as sodium alginate and potassium alginate, are produced by extracting polysaccharides, which is contained in brown algae, and processing the polysaccharides as required. Currently, as an application for a food product, the sodium alginate is widely and generally used mainly as a stabilizer for a frozen dessert. Additionally, applying reactivity of the alginate to calcium ion, an imitation food pectized as integuments of an artificial salmon roe and a caviar, a regenerative food such as onion rings, and a similar food product have been used.
A calcium-reaction gel of sodium alginate has properties of thermal irreversibility and heat resistance, which are not possessed by other pectizing agents. However, it is almost impossible to cause sodium alginate aqueous solution that the sodium alginate dissolved in water to uniformly react to calcium ion to produce a uniform gel. This is because of the following reason. Alginic acid ion reacts to the calcium ion in a blink. In view of this, the alginic acid ion promotes the reaction at a part in contact with calcium solution. Accordingly, as the calcium ion does not penetrate as being away from an interface with the calcium solution, the alginic acid ion fails to react to the calcium ion. As a result, even if calcium alginate gel is produced and the outside of the calcium alginate gel is hard and hydrophobized, the calcium ion does not penetrate to the inside of the calcium alginate gel and therefore the reaction does not proceed. Thus, a soft gel is formed. This gel is not uniformed even being left for a while. Thus, obtaining the uniform gel of calcium alginate is not easy. There is also a conventional problem of requiring an extremely complicated manufacturing process for manufacturing gels.
A dried product formed by drying the calcium alginate gel, for example, a dried product formed by freezing the calcium alginate gel for denaturation and then dehydrated and dried becomes the dried product where an insoluble fiber is hydrophobized. Thus, the dried product that is hardly restored is formed. In view of this, calcium alginate that has a dried form does not exist as a conventional food material. Although powder of the calcium alginate formed by replacing the sodium alginate with the calcium ion has been developed into a product, this is completely an insoluble and therefore has no restorability (imbibition). This limits the application of the powder.
On the other hand, agar, which is an extracted material similarly derived from seaweed, is dissolved in hot water and is uniformly pectized by cooling. The agar has a property of thermal reversibility. When heating the gel to 90 to 100° C., the gel is reconstituted to a sol, thus forming a solution. In view of this, the agar is not suitable for an application where the gel state is maintained and requires the heat resistance. In particular, recently, as a food material, the dried product made of the agar is produced. This is used by being reconstituted (imbibed) in cold water and warm water. However, these food materials are melted by heating to 90 to 100° C., which is a dissolution temperature of agar. A heat-resistant agar is also available. However, restorability (imbibition) of such agar in cold water and warm water is insufficient. This has problems of, for example, causing the agar to be tasted dried out and a flavor of food is not balanced.
Various studies have been conducted on a food product containing the agar and the alginate. For example, Patent Literature 1 discloses a dried rice-shaped food product mainly constituted of agar and alginic acid or alginate and formed into a rice shape. A ratio between the agar and the alginic acid or the alginate is 9:1 to 1:9. For example, Patent Literature 2 discloses a method for manufacturing a heat-resistant pectized food product that heats and dissolves a pectizing agent that has a property of being pectized by reacting to cation and a pectizing agent that has a property of being pectized by cooling without reacting to the cation. Then, the materials are cooled so as to be pectized. The obtained pectized material is shaped into an appropriate size as necessary. The pectized material is then dipped in a solution containing cation to further progress the pectization. Patent Literature 3 discloses a gel-like processed food product formed by pectizing a sol containing alginates and agar.
Patent Literature 4 discloses a noodle-shaped food product. The noodle-shaped food product is formed as follows. Sodium alginate is added to a soybean concoction and is formed into a noodle shape. The material is then discharged into a calcium solution and is coagulated. Then, the material is processed in a solution containing salt. When the gel adjusted as a result of a reaction of the sodium alginate and calcium salt (such as calcium chloride) is in contact with water solution containing a salt content, the gel softens and therefore the strength is degraded.
Further, Patent Literature 5 discloses a dried food and a method for producing the dried food. The dried food contains agar as a main agent and at least one kind of an auxiliary agent selected from alginic acid and a similar material. As a concrete example, the dried food at a weight ratio of the agar to the sodium alginate being 90/10, namely, 1:0.11 is disclosed (Working example 6). Patent Literature 6 also discloses a dried agar food ready for eating by reconstitution in water or in hot water and a method for producing the dried agar. To enhance the heat resistance, an auxiliary agent such as alginic acid may be dissolved. Then, saline such as Mg may be added to be reacted. Finally, the material may be mixed in a filtrate of the agar.